MHD Stability of Fusion Plasma with Ferromagnetic Wall Effect

在发展聚变DEMO反应堆中的两个重要问题是实现高β等离子体和低活化材料的发展。在低活化材料方面，铁素体钢被认为是最有希望作为DEMO反应器结构材料的候选材料。然而，由于铁素体钢具有强的铁磁性，它也被认为对等离子体的点火、控制、MHD稳定性和等离子体约束等有不利影响。其中，MHD稳定性直接关系到高β等离子体的实现，铁素体钢有可能恶化MHD稳定性，降低临界β值。因此，研究铁磁效应对磁流体动力学稳定性的影响是聚变堆发展中的重要问题之一。本研究的目的是探讨铁磁效应对临界β的影响，在小纵横比和圆截面平衡的情况下， ...更多信息 使用线性MHD稳定性代码，它使用电阻MHD方程的完整集合。在这些研究中获得的结果如下：铁磁性的影响的临界β的减少被证明是8%和20%，分别对相对磁导率为2和3的铁磁壁，对于纵横比为3的托卡马克。对于高深宽比托卡马克，对相对磁导率为2的铁磁壁，减小值为10%，认为环形效应对临界β的铁磁效应很小。结果表明，由于壁面铁磁性引起的扰动极向磁场的吸引作用，使外扭折模不稳定，临界β值降低，环向等离子体旋转和等离子体耗散效应在阻性壁小半径处打开了稳定窗口，而在高深宽比托卡马克中未观察到.稳定窗口的宽度被示出为在相对渗透率小于3的小值中加宽，而稳定窗口的宽度被示出为在相对渗透率大于3的大值中减小。稳定化效应是由于铁磁性降低了非稳定模与稳定模的还原速率，从而使非稳定模与稳定模耦合。少

Two important issues in developing the fusion DEMO reactor are the realization of high beta plasma and the development of low activation materials. As for the low activation materials, the ferritic steel is considered to be the most promising candidate as the structural material in DEMO reactor. Because of its strong ferromagnetism, however, the ferritic steel is also considered to have a bad influence to plasma ignition, control, MHD stability and plasma confinement etc.. Among others, MHD stability is related directly to the realization of high beta plasma, and the ferritic steel has possibility to deteriorate MHD stability and decrease the critical beta value. It is, therefore, one of the most important issues in development of fusion reactor to investigate the ferromagnetic effect on the MHD stability. The purpose of this study is to investigate the effect of ferromagnetic effect on critical beta by MHD stability analyses for low aspect ratio and circular cross section equilibrium … More using linear MHD stability code, which uses the full set of resistive MHD equations. The obtained results in these studies are in the following :The reduction of critical beta by the effect of ferromagnetism is shown to be 8 % and 20 % against the ferromagnetic wall of relative permeability of 2 and 3, respectively, for tokamaks of aspect rate 3. The reduction value is 10 % against the ferromagnetic wall of relative permeability of 2 for high aspect ratio tokamaks, and the toroidal effect is considered to be small for ferromagnetic effect on the critical beta. It is shown that the attraction of the perturbed poloidal magnetic field due to ferromagnetism in the wall destabilizes the external kink mode, and reduces the critical beta values.The existence of the stability window in the minor radius of resistive wall opened by both effects of the toroidal plasma rotation and the plasma dissipation is shown for tokamaks of aspect ratio 3, while they have not been observed for high aspect ratio tokamaks. The width of stability window is shown to be widened in small values of relative permeability less than 3, while it is shown that the width of stability window is reduced in large values of relative permeability greater than 3. The stabilization effect comes from the coupling the unstable mode to the stable mode, whose reduction rate is decreased by the ferromagnetism. Less